A 5-post backframe is the first indicator that a manufacturer has taken the design of a piano seriously. However, the thickness of the individual back posts matters. A cross sectional surface area of 400cm2 or more provides massive support year after year for the the soundboard’s crown and the nearly 40,000lbs of tension from the strings. The CSA is calculated by multiplying the width and depth of a post, times the number of posts, and it is a good indicator of an upright piano’s structural integrity. The cheapest pianos will have very small backposts or no center backposts at all.